160mph clocks into 120mph

[Jay]

Percentages and pie charts init 

[danj3000]

Well my speedo has always read about 40 when i'm actually only doing 30 - one of the eccentricities of the car i guess.
I imagine this could be down to the wrong gear pinion? even though it had it replaced about 18 months ago - before i got the car i may add.

Also my speedo has started reading strangely the last week. It over reads by a large margin eg. 50 when doing 25-30. It will then hang around there even if i start slowing. Could it be that the speedo cable is slipping? and could i cure this by greasing it up or would it mean a new one?

ta very much 

[Jay]

Might as well replace it while you have the clocks out, it will probably just save you time in the future.

[rubjonny]

that'll be the speedo thats duff, cable is always spinning at the same speed as the output shaft on the gearbox.  You can check your speedo with reasonable accuracy using the scirrocco.org gear ratio calculator:
http://scirocco.org/gears.

[danj3000]

When you say the speedo is duff runjonny, do you mean the clocks, cable or the speedo drive in the gearbox end?

[rubjonny]

I mean the speedo
the actual clocks are just fine, just the speedo part thats bust

[danj3000]

okies, thats a part i need to get from a VAG dealer is it not? If you had the part number that would be awesome! 

[rubjonny]

i wouldnt, cost a bomb.  get another set o clocks off ebay or summat, fiddle the milage and fit!  either get a set o clocks that are a direct fit, or any clocks with a speedo the same as yours, just match up the # of plugs on the bottom, pre/post 90 speedos are different round the back

[danj3000]

ok then, so you think it would be the speedo clocks then - i thought you meant the little gear situated in the gearbox which the speedo cable gets its drive from. I thought it could be this as an old fiesta of mine had this issue and wore the little pinion, thus getting crappy if any reading from the speedo.

If i swapped the speedo over from the 16v (pre 90)  i have then you reckon that would rectify the dodgy reading i'm getting?

Also i'm pretty sure i've seen somewhere you can dismantle the speedo and take out the mileage reading and simply change that over to the other speedo - is this right?

[rubjonny]

well the speedo works by reacting to the speedo cable spinning, there would be no way for the speedo cable to carry on spinning at 50 mph as the car is slowing down, so its got to be the speedo itself sticking.  I adjusted the milage in my 16v speedo without even taking the dial face off, I did have to remove it from the clocks though.

As long as both clocks are the same type (pre or post 90) then the speedo will swap over.  Doesnt even have to be the same make, in my driver I had a motormeter speedo in vdo clocks!